1. Field of the Invention
This invention relates generally to a vehicular apparatus for detecting rotational imbalance of the unsprung mass of a vehicle. More particularly, the present invention relates to an apparatus which utilizes a force sensor to dynamically determine the rotational imbalance of the vehicle unsprung mass.
2. Disclosure Information
A vehicle having one or more imbalanced roadwheel assemblies often suffers from the potential problems of excessive tire wear, misaligned wheel positions and degraded steering and handling characteristics. Often, a vehicle operator has no clear indication that any of the vehicle wheels are out of balance until significant problems have already developed, resulting in the repair or replacement of worn vehicle parts. Therefore, it would be beneficial to warn the vehicle operator if any of the vehicle roadwheel assemblies, both steered and nonsteered, are out of balance so that the imbalance may be corrected before permanent damage occurs. Furthermore, with the advent of active suspension systems, it is very important to detect whether any vehicle roadwheel assembly is out of balance so that the active suspension actuator does not continuously operate to dampen the vibrations due to the rotational imbalance and hence cause a loss of power and gas mileage to the vehicle.
My U.S. Pat. No. 4,907,452, assigned to the assignee of the present invention, discloses a system for dynamically detecting the rotational imbalance of the steerable roadwheel assemblies of a vehicle. The system utilizes a force sensor for measuring the force required to steer the steerable wheels of the vehicle in determining whether the wheels are imbalanced. That system suffers from the disadvantage that the rotational imbalance of some types of nonsteered wheels of the vehicle can not be measured. That system also presents a disadvantage to vehicles having active suspension systems in that the nonsteered wheels continuously create vibrations to the vehicle body caused by the rotational imbalance which the driver may never feel because the active suspension actuators dampen the vibrations. Furthermore, that system requires an additional steering force sensor not normally present in the vehicle. The present invention provides an improvement to the '452 system in that the present invention detects if any roadwheel assembly of the vehicle is out of balance. The present invention utilizes a force sensing device interposed between the sprung and unsprung masses of the vehicle to detect rotational imbalance of a roadwheel assembly. As used herein, " sprung mass" refers to the body or chassis of the vehicle while "unsprung mass" refers to the roadwheel assembly and associated rotating members.
Many systems have been proposed which detect abnormal conditions in the operating state of the vehicle roadwheel assemblies. For example, U.S. Pat. Nos. 2,720,638; 3,526,873; 3,744,321; and 4,458,535 all disclose systems utilizing vibration sensors to detect abnormalities in the vehicle wheel due to any number of conditions, such as a flat tire or low tire pressure. However, none of the systems teach or suggest any way to dynamically detect whether any of the vehicle roadwheel assemblies are rotationally imbalanced using a force sensor according to the present invention.
U.S. Pat. No. 4,463,936 discloses a system in which steering pressure is measured to indicate a vehicle operating condition wherein the leaves of a multileaf suspension spring will be clamped to change the damping characteristics of the suspension. U.S. Pat. No. 4,470,260 discloses a system in which hydraulic steering pressure is sensed and used as a control variable in a system which controls the kickback of an open center, load sensing hydraulic steering apparatus. None of the aforementioned patents discloses a system in which force is measured and employed in a system for determining the rotational imbalance of the vehicle roadwheel assemblies.
U.S Pat. No. 3,438,646 discloses a system for detecting alignment changes on a vehicle, but does not disclose detection of imbalance roadwheel assemblies. U.S. Pat. No. 4,719,445 discloses a system utilizing statistical methods to determine whether the position and motion of a steering linkage are correct. The system employs a single sensor on the steering linkage and does not measure force exerted between the road surface and the vehicle sprung mass as does the present invention.
It is an object of the present invention to provide a system which dynamically detects rotational imbalance of vehicle roadwheel assemblies so that corrective measures may be taken before the dynamic imbalance causes permanent damage to the vehicle.
It is an advantage of the present invention that a system according to this invention may be employed not only with conventional suspension systems but also with active and semi-active systems.
It is yet another advantage of a system according to the present invention that this invention may be employed for determining the absolute magnitude of a weight imbalance affecting both steered and nonsteered roadwheel assemblies and to diagnose the cause of the imbalance as originating in either the roadwheel assembly or its associated rotating members.
Other objects, features and advantages of the present invention will become apparent from the drawings, description and claims which follow.